A storage system is configured by comprising at least one or more storage apparatuses referred to, for example, as disk array subsystems. With this type of storage apparatus, disk drives such as hard disk drives and semiconductor memory drives are arranged in an array to provide storage areas that are operated in RAID (Redundant Array of Independent Inexpensive Disks) format. A host computer (this is hereinafter referred to as the “host”) accesses the storage areas provided by the storage apparatus and thereby performs the reading and writing of data.
Incidentally, the amount of data that is being managed in organizations such as corporations, local governments, educational institutions, financial institutions and public offices is of an annually increasing trend, and storage apparatuses are being added or replaced pursuant to the increase in the amount of data. In light of the increase in the amount of data and the complication in the configuration of the storage system, PTL 1 discloses technology of arranging, in order to improve the utilization efficiency of the storage system, data to be used by various application programs such as email management software and database management software at an appropriate location according to the value of such data, defining a plurality of different device hierarchies in the storage apparatus, and rearranging the data in the storage apparatus among the device hierarchies (this is hereinafter referred to as “data migration” or “hierarchy control”).
Meanwhile, although the storage capacity of a logical volume is generally fixed, PTL 2 discloses technology of automatically expanding the storage capacity of a virtual volume by allocating a partial page of a physical resource (this is hereinafter referred to as the “physical page”) to that virtual volume according to an access request from a host computer in order to increase the utilization efficiency of the storage areas. In the ensuing explanation, a partial page in the virtual volume corresponding to the physical page is hereinafter referred to as a “virtual page.”
The virtual volume is a hypothetical logical volume. The storage apparatus is able to show the host (more precisely, the application that is executed by that host) a virtual storage capacity (this is hereinafter referred to as the “virtual capacity”) which is different from the total storage capacity (this is hereinafter referred to as the “real capacity”) of one or more physical pages that are actually allocated to the virtual volume.
As a result of a physical page being allocated to a virtual volume, the real capacity of the virtual volume will be expanded in the amount of the storage capacity of that physical page. Thus, the virtual volume can also be referred to as a “capacity-expanded volume.” In addition, since the virtual volume is also a logical volume that can be provided based on the Thin Provisioning technology, it can also be referred to as a “Thin Provisioning volume.”
The logical volumes in a storage apparatus are sometimes backed up in order to prepare for data loss and the like caused by the malfunction of a disk drive. PTL 3 discloses technology of copying only a virtual page corresponding to a physical page that was allocated to a virtual volume to a tape in a tape library device upon backing up a virtual volume in a tape library device, and copying only the virtual page in the copied tape to a storage apparatus upon restoring data from the tape library device.